Comments

There is so many variables to this, that I cannot give any solid statement on this cause. The shooting style might have changed or your hardware even the settings of alignment. What I can suggest you is, according to how you mentioned you combine sets would be settings the image overlap to Low, Detector sensitivity to High and raising the number of features for detection to lets say 60,000. This would make for a more detailed inspection of the alignment algorithm, also counting on the images being far from each other as you use drone and dslr. Not saying this would make miracles but it might help your case.